The molding compounds with which we are concerned utilize a crosslinking thermosetting polymer as a matrix material and may include fillers and/or fibers to strengthen and/or cheapen the product. The molding compounds usually include an activating catalyst for the crosslinking process, and a mold release agent which prevents these materials from bonding to the metal dies used in the molding process. Great economy is achieved by reason of the simultaneous shaping and curing of the molding compounds to a thermoset condition. Molding compounds are dependent, however, upon the presence of a mold release agent to prevent the crosslinking of the molding compound from adhering to the surfaces of the forming molds. The precise mechanism by which mold release agents operate is not known. One theory which has been held heretofore is that there is a migration during cure of the mold release agent to the heated surface of the mold to create a non-adhering film on the surface of the molded part produced. Whether or not this theory is correct, has to the writer's knowledge, never been settled. It is axiomatic, however, that without the presence of the mold release agent, molding compounds stick tenaciously to the surface of untreated molds, and that with the mold release agent present, they do not stick to the surfaces of untreated molds. It is not always feasible to put lubricant on the surface of molds between the times that each part is made, so that molding compounds which are used for commercial production usually include a mold release agent, usually a salt of a fatty acid.
Certain problems exist with parts that are molded from compounds that contain mold release agents in that paints and/or subsequent pigmented resinous surfacing layers cannot be bonded thereto without the removal of the film of mold release agent that exists on the molded part. Removal of the film of mold release agent is usually done by sand blasting, sanding, scraping, etc.. A method used to produce colored parts without this removal step has been to incorporate pigment in the molding compound. The incorporation of the pigment in the molding compound, however, is wasteful of the pigment. Production of different pigmented molding compound is also more tedious.
An object of the present invention is the provision of a new and improved process whereby molding compounds containing mold release agents can be molded, and a highly pigmented coating applied thereto, without any additional preparation of the surface of the molded part before the coating is applied.
Another object of the invention is the provision of a new and improved process of the above-described type wherein the coating can be applied in the same set of dies in which the main body portion was molded.
Another object of the present invention is the provision of a new and improved method of bonding two separate layers of molding compounds even though they contain mold release agents.
Further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the following description of the preferred embodiments.